The present invention relates to an automatic adjustment system and method for audio devices and specifically to such systems for performing acoustic correction of audio signals generated by audio devices.
Systems and methods for making acoustic adjustments of audio devices to tailor sound to suit a particular environment or listener's taste are known. For example, automobile audio systems that can be adjusted to tailor their sound output for the environment of a particular automobile, or for a type of music and musical taste are known art.
One of the motivations for making such acoustic adjustments is to achieve optimal sound quality in different environments. For example, different automobile interiors can have widely different shapes, materials which affect sound heard by passengers and driver. Interceding objects may also affect sound distribution and quality. To achieve ideal results in automobiles, acoustic corrections must be performed for each installation, since no two automobiles are identical. A corollary is, if acoustic adjustments are performed identically for every automobile, the acoustic results will not be identical from one automobile to another.
Such acoustic adjustment systems and methods generally employ a parametric equalizer connected to the audio system whose sound is to be altered. The parametric equalizer divides an audio signal into a number of frequency bands and selectively amplifies and attenuates each frequency band to achieve a desired sound quality. The series of amplifications and/or attenuations across a range of frequencies is called the equalizer data. Each of the frequency bands of sounds passing through the parametric equalizer is changed according to the equalizer data. A technician or user listens to recorded sounds passing through the parametric equalizer and inputs the equalizer data accordingly. To make the technician's adjustments more precise, the technician may use a digital sound processor to analyze the audio passing through the parametric equalizer while making the adjustments.
The inputting of the equalizer data may amount simply to the adjustment of a series of potentiometers, if the parametric equalizer is non-programmable. Equalizer data for a programmable parametric equalizer would be entered by manually keying in and storing the equalizer data.
Generally, a specialist, at an automobile or audio system retailer, would perform the above adjustments. The specialist must listen to sounds generated by the system after it is installed, determine the corrections to be made by trial and error, and store the required sound alteration parameters in a memory. A series of manual adjustments of the device may likewise be used by the specialist for this purpose.
In a prior art audio device, there is no way for the adjuster to know the desired frequency-response of the owner. The desired frequency response is the goal of the acoustic correction of the sounds actually generated by the speakers. Thus, if for some reason the settings previously stored in the memory of the device are lost, much trial and effort would be required to obtain the result desired by the owner to restore an identical acoustic space. Moreover, there is no way to know if the acoustic space is identical to the previous one or not.
A modern stereo audio system may have multiple channels, each directed to a particular speaker. For example, an automobile audio system might have subwoofers, low, mid and high range speakers in the front and low, mid and high range speakers in the rear. The arrangement is replicated for each of left and right stereo channels. Thus an automobile could have as many fourteen channels of sound to output, each having its own power amplifier. To insure that sound output by the audio system is balanced and that the desired frequency response is achieved, the respective gains of such a network of power amplifiers must be properly adjusted.
The installation of such prior art systems with their complex channel networks is plagued by other difficulties. Additionally, the prior art is complicated by a need for a procedure for connecting the channels of the power amplifiers to their respective speaker elements. As stated above, there may be fourteen or more different channels to connect correctly. This complexity tends to produce connection errors. In addition, to confirm the channel connections, it was possible to see if the speaker was on the right or the left or the front or the rear by manipulating the fader and balance controls. However, the connections to the different speaker elements located at a given location, i.e. the low-range, mid-range and high-range speaker elements, cannot be confirmed this way.
Another problem with regard to making and checking speaker connections is the polarity of the speaker connection. In any audio system, it is desirable for the amp and the speaker to be connected with the correct respective + (positive) and - (negative) polarities. If these polarities are incorrectly connected, the audio output from the speaker will be inverted, and the resulting sound quality can be significantly decreased. Operating manuals and other guides generally contain warnings admonishing the installer to connect the amp and the speaker carefully.
In addition, in prior art audio devices, if the power supply of the audio device is not turned off when the amp and the speaker are connected, there is a possibility that the audio device could be damaged. Since the correctness of the connection is frequently checked after connection by listening to the sound coming from the speaker, checking is difficult, especially when many speakers are involved.
Furthermore, some users consciously made reverse-polarity connections for certain types of music so they could enjoy the abnormal sound quality. However, making such changes is difficult because it entails changing the wiring of the speakers.
One of the problems with setting equalizer data such as cut-off frequencies, frequency-response slope limits, etc. is that such data must be set by actually listening to the sound from the speakers. There was no way for a system adjuster to know the actual network band widths accurately. Even using a device capable of measuring frequency response, only the end result of the adjustments could be known to the adjuster. Devices known in the prior art are only capable of indicating the equalizer data numerically. Such an indication does not lend itself to giving an adjuster feedback regarding the present settings of the parametric equalizer.
The prior art technology has several shortcomings. Adjusting the parametric equalizer's parametric data while listening to sounds generated by the audio device may be inordinately time-consuming. In addition, the result achieved can vary depending on the type of sounds (music, for example) used to make the adjustments. Moreover, variability can result from changes in the skill or personal bias of the specialist. Such variability can make consistent adjustment of audio systems difficult to achieve. Conventional devices do not adequately address this issue.
Another problem with the prior art is that correction data, if lost from memory, cannot be restored without redoing the acoustic adjustments. Once readjusted, because of the variability of specialists and other circumstances, the result may not be identical to the settings that were lost.
Still another problem with prior art systems is that adjustments appropriate for a particular car are made by changing the gain for each of a number of different channels of the power amplifier corresponding to the different speaker units. According to the prior art system, this is done by listening to the sound from the speakers and adjusting the volume of the power amplifier with a screw driver or knob. The process of adjusting the amplifier gain while actually listening to the sound from the speakers is difficult and tedious. In addition, the adjustment of a power amplifier, which, in a car, is typically mounted in the rear or the trunk, is very awkward after the amplifier has been mounted. Moreover, to adjust the gains of each channel of the power amplifier to achieve a desired balance, or other relationship therebetween, is a particularly onerous task with the prior art audio system.
The balancing of gain of the different channels involves a number of comparisons. The gain levels of front and rear speaker banks in an automobile audio system must be adjusted to provide a desired balance of the resultant output. The gain of each channel, each of which may drive a speaker corresponding to a different range of frequencies, must be adjusted so that the results of parametric equalization can be realized. In other words, the gains of the channels connected to the woofer speakers must be adjusted independently of the gains of the channels connected to the tweeter speakers. All of the channels gains must be adjusted so that the parametric equalizer can achieve a desired result. For example, if the gain of a tweeter channel is too high relative to a woofer channel, the desired frequency response characteristic cannot be obtained.
The display of sound level data, such as frequency response, can enhance the adjustment of the settings of the parametric equalizer by providing feedback to the user. However, frequency response data can be overwhelming, particularly when it is desired to understand the front, rear left and right channel outputs independently of each other. This is especially true since acoustic correction for the left channel and right channel the sounds output from the speakers on the front side or the rear side are for both channels combined.
It is nearly impossible to make sense of frequency response data by listening to one channel at a time because the channels are combined during normal listening. Furthermore, the average levels of the channels could not easily be adjusted using only the frequency response data because such data does not lend itself to comparing the different channels overall.
Aside from balancing the gains of each channel, the course adjustment of the absolute value of amplifier gain in prior art devices performed manually is generally done in the same way. The adjuster must listen to the sound coming from the various speakers and manually adjust the amplifier gain so the resulting sound output is within a certain range. If the gain is insufficient, the sound output will not be up to the rated capacity of the audio system. If the sound output is too high, a poor sound quality may result. The manual adjustment of the gain of each amplifier channel entails a great deal of time. In addition there is a risk of inaccuracy because of personal bias of the adjuster or idiosyncracies in the adjuster's sense of hearing.
In addition to being difficult to perform, network adjustments for balancing sound levels between front and rear and left and right channels are also time-consuming. This problem is likewise prone to human bias and error. To install sophisticated audio devices in cars, a specialist must make adjustments which involve some degree of personal judgement and store the results of his adjustments in the programmable parametric equalizer and amplifiers. If, for some reason, the adjustment data stored in the memory of the audio device is lost, it is necessary to go to the specialist at the tuning shop where the adjustments were made and have the whole adjustment process redone.